1. Field of the Invention
This invention relates generally to photonic integrated circuits (PICs), including electro-absorption modulators/lasers (EMLs), and more particularly to electrical isolation of electro-optical components in such circuits.
2. Description of the Related Art
In photonic integrated circuits or PICs, two or more active or electro-optical components as well as possibly at least one passive optical component are generally integrated on a single semiconductor or other type of chip. A well known example of this kind of PIC chip is an EML (Electro-absorption Modulator/Laser) where, for example, a distributed feedback (DFB) laser is integrated with an electro-optical modulator such as illustrated, for example, in U.S. Pat. No. 6,148,017, employing the InGaAsP/InP regime. There are many such examples of EMLs in the art and this just one recent example of this type of device. In order that there is no electrical interference between the operation of these integrated electro-optical components, an electrical isolation region (which is shown at reference number 5 in the above mentioned patent), which is usually an isolation trench, is generally deployed between such optical components. The trench usually extends down into the bulk of the PIC chip as far as the upper confinement layer, for example, above the active region of the PIC chip. However, it is desirable not to extend such a trench too far into the chip so as to perturb the optical mode propagating in the active region of the device as well as cause significant backward reflections of the optical mode since such a trench can function as a partial mirror to the propagating mode.
These types of EMLs suffer from lack of good electrical isolation between the optical modulator and the DFB laser because the trench is still not deep enough to provide good avoidance of electrical interference, particularly in the separation of the operation of the DFB laser from the electrical modulation of the optical modulator. In particular, parasitic current paths still exist between these electro-optical components. For example, in EMLs, a parasitic path will exist below the isolation trench between the DFB laser and the electro-optical modulator such that the DFB laser will experience fluctuation changes in its drive current via the fluctuations of the parasitic current established between the laser and modulator. This modulated parasitic current perturbs the operation of the DFB laser. As indicated above, generally the isolation trench cannot be made deeper into the PIC chip in an attempt to further electrically isolate the DFB laser from the optical modulator without affecting the properties of the propagating optical mode.
It an object of the present invention to overcome the aforementioned problems.
It is a further object of this invention to provide for electrical isolation particularly between electro-optical components in a PIC, such as an EML without affecting the propagating optical mode in the PIC.
According to this invention, an electrical isolation region is formed between adjacently disposed electro-optical components integrated in a monolithic semiconductor photonic chip, such as an EML or PIC chip, wherein a bias, VC, is applied to the isolation region so that any parasitic current path developed between adjacently disposed electro-optical components, now separated by the isolation region, is established through the electrical isolation region and clamped to the bias, VC. The applied bias, VC, may be a positive bias, a negative bias, or a zero or a ground bias. While EMLs have been exemplified herein, other electro-optical devices integrated on a semiconductor chip may also be benefited by the isolation region utilized in this invention, such as, for example, a photodetector (PIN) photodiode or avalanche photodiode (APD)), a semiconductor optical amplifier (SOA) or a gain clamped semiconductor amplifier (GCSOA), also referred to as a semiconductor laser amplifier, as well as a semiconductor electro-absorption modulator (EAM), Mach-Zehnder modulator (MZM), DFB laser or DBR laser.
In a particular embodiment of this invention, the electrical isolation regions are formed by spatial current blocking regions formed at adjacent sides of the electrical isolations region transverse to a direction of light propagation through electro-optic components and/or optical passive components formed in the PIC chip, or said another way, between each electrical isolation region and an adjacent optical component which all integrated into the PIC chip. The spatial current blocking regions sandwiching the electrical isolation region is coupled to bias, VC, for capturing any parasitic current flow between the electro-optic components or optical passive components in the PIC chip. The preferred embodiment for spatial current blocking regions herein is spatially disposed trenches between which the electrical, biased isolation region of this invention is achieved. However, it is within the scope of this invention to provide such isolation regions utilizing means other than trenches, such as by forming insulating regions via doping, e.g., Fe doping, or via ion implant, e.g., H+ implantation, or other processes or structures that would form such an electrical isolation region.
While general mention here is made of active or electro-optical components and their electrical isolation from one another, it should be understood that the isolation regions of this invention may also be utilized between active and passive optical components formed in a PIC chip, such as between PIN photodetectors or electro-optical modulators and an optical combiner (multiplexer), such as an arrayed waveguide grating (AWG), where the refractive index of the latter can be affected by induced parasitic current paths established from such active devices to the passive device changing slightly its waveguide properties due a to slight change in refractive index in at least a portion of the passive device due to such parasitic current flow.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.